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BACKGROUND: Cardiac fibrosis is a common pathological feature associated with adverse clinical outcome in postinjury remodeling and has no effective therapy. Using an unbiased transcriptome analysis, we identified FMO2 (flavin-containing monooxygenase 2) as a top-ranked gene dynamically expressed following myocardial infarction (MI) in hearts across different species including rodents, nonhuman primates, and human. However, the functional role of FMO2 in cardiac remodeling is largely unknown. METHODS: Single-nuclei transcriptome analysis was performed to identify FMO2 after MI; FMO2 ablation rats were generated both in genetic level using the CRISPR-cas9 (clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeat–associated 9) technology and lentivirus-mediated manner. Gain-of-function experiments were conducted using postn -promoter FMO2, miR1a/miR133a-FMO2 lentivirus, and enzymatic activity mutant FMO2 lentivirus after MI. RESULTS: A significant downregulation of FMO2 was consistently observed in hearts after MI in rodents, nonhuman primates, and patients. Single-nuclei transcriptome analysis showed cardiac expression of FMO2 was enriched in fibroblasts rather than myocytes. Elevated spontaneous tissue fibrosis was observed in the FMO2-null animals without external stress. In contrast, fibroblast-specific expression of FMO2 markedly reduced cardiac fibrosis following MI in rodents and nonhuman primates associated with diminished SMAD2/3 phosphorylation. Unexpectedly, the FMO2-mediated regulation in fibrosis and SMAD2/3 signaling was independent of its enzymatic activity. Rather, FMO2 was detected to interact with CYP2J3 (cytochrome p450 superfamily 2J3). Binding of FMO2 to CYP2J3 disrupted CYP2J3 interaction with SMURF2 (SMAD-specific E3 ubiquitin ligase 2) in cytosol, leading to increased cytoplasm to nuclear translocation of SMURF2 and consequent inhibition of SMAD2/3 signaling. CONCLUSIONS: Loss of FMO2 is a conserved molecular signature in postinjury hearts. FMO2 possesses a previously uncharacterized enzyme-independent antifibrosis activity via the CYP2J3-SMURF2 axis. Restoring FMO2 expression exerts potent ameliorative effect against fibrotic remodeling in postinjury hearts from rodents to nonhuman primates. Therefore, FMO2 is a potential therapeutic target for treating cardiac fibrosis following injury.

Objectives The present study aimed to explore the major factors that account for the beneficial effects of mesenchymal stem cells (MSCs). Methods Using isobaric tags for relative and absolute quantitation method, hepatoma-derived growth factor (HDGF) was identified as an important factor secreted by MSCs, but not by cardiac fibroblasts (CFs). The protective effects of conditioned medium (CdM) from MSCs or CFs were tested by using either H9C2 cells that were exposed by hypoxia-reoxygenation (H/R) insult or an in vivo mouse model of myocardial ischemia-reperfusion. Results Compared to CF-CdM, MSC-CdM conferred protection against reperfusion injury. CdM obtained from MSCs that were treated with HDGF-targeted shRNA failed to offer any protection in vitro. In addition, administration of recombinant HDGF alone recapitulated the beneficial effects of MSC-CdM, which was associated with increased protein kinase C epsilon (PKCε) phosphorylation, enhanced mitochondria aldehyde dehydrogenase family 2 activity, and decreased 4-hydroxy-2-nonenal accumulation. A significant decrease in infarct size and ameliorated cardiac dysfunction was achieved by administration of HDGF in wild-type mice, which was absent in PKCε dominant negative mice, indicating the essential roles of PKCε in HDGF-mediated protection. Conclusions HDGF secreted from MSCs plays a key role in the protection against reperfusion injury through PKCε activation.

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Introduction: Myocardial infarction (MI) is characterized by cardiac dysfunction and increased cardiomyocyte death, induced mainly by apoptosis. Using an unbiased transcriptome analysis, we identified flavin containing monooxygenase 2 (FMO2) as one of the top-ranked genes involved in the process of MI. In this study, we investigate the roles of FMO2 in ischemic injury and its potential mechanisms. Hypothesis: FMO2 exhibits the cardiac protection from MI injury. Methods: Male SD rats receiving either adeno-associated virus serotype 9 containing FMO2 shRNA particles (AAV-shFMO2) or FMO2 (AAV-FMO2), and FMO2 knockout rats were subjected to myocardial infarction surgery. Cardiac function, fibrosis, and apoptosis were examined in these rats and related cellular and molecular mechanisms were investigated. Results: Cardiac ischemia injury was associated with significant increases of FMO2 levels both in ex vivo and in vivo models. Loss of FMO2 significantly enhanced cardiomyocyte apoptosis and deteriorated cardiac function accompanied by augmented infarct size in infarcted rat hearts, while elevated expression of FMO2 exhibited the opposite results. Mechanically, located on the ER membrane, FMO2 inhibited activation of ER stress-initiated apoptotic proteins including caspase 12 and C/EBP homologous protein (CHOP), via down-regulating upstream unfolded protein response (UPR) pathway. Furthermore, we found that FMO2, as a novel chaperone in ER, directly catalyzed disulfide-bond synthesis to facilitate proteins folding. Finally, structure analysis of FMO2 revealed the active site GVSG for disulfide-bond catalysis, which was confirmed by the molecular docking experiment of GSH with FMO2. However, FMO2 with GVSG mutation failed to catalyze disulfide-bond formation and lost protection from ER stress or apoptosis in cardiomyocytes. Conclusion: FMO2 confers cardiac protection from ischemic damage due to improved cardiomyocyte apoptosis through UPR pathway, which is mediated by disulfide-bond catalysis at GVSG active site. Our findings uncover a novel FMO2-involved regulatory mechanism which could serves as a potential therapeutic target for ischemic cardiovascular diseases.